Evaluation and Discussion of Extra-Long-Section Extra-Multicluster Hydraulic Fracturing Technology for Shale Gas Horizontal Well Based on Flow Scanner Image

Abstract

Abstract Fuling Shale Gas Field (FSGF) was the first commercially developed large scale shale gas field in China. The main field target layer is located in the upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation in Sichuan Basin. The field is characterized by great geological age, thin high-quality reservoir, high compaction degree, and strong heterogeneity. With the application of volumetric stimulation technology over the past 10 years, a certain breakthrough has been made in the post-frac production rate. Some fracturing schemes have been formed, suitable for the development of a Fuling Shale Gas Field. However, to further improve the comprehensive development efficiency of shale gas reservoirs and reduce the cost of fracturing, a pilot experiment of "extra-long-section extra-multiclusters and temporary plugging turning" fracturing technology was carried out in well JYxx-8HF. The goal was to expand the effective stimulation volume, improve fracture complexity, and ensuring fracturing fluids enter each cluster evenly. The length of the horizontal well section of JYxx-8HF is 2,500 m with a total of 112 perforations and clusters, divided into nine stages for hydraulic fracturing. The max. section spacing of a single stage is 329 m. The average section spacing of a single stage is 221 m. The max. number of clusters in a single stage is 20 clusters. The average number of clusters in a single stage is 13.5. Compared with the traditional 20-stage with 4–5 perforated clusters per stage of FSGF, the fracturing program of this well is bold and innovative. Three records were set with the highest liquid volume in single-stage, the highest sand volume in single-stage, and the largest number of perforation clusters in single-stage in China. Horizontal and deviated well production logging System™ (FSI) is a state-of-the-art production logging platform. It can measure the flow velocity and fluids holdup of three-phase flow along the vertical section of the wellbore by five mini-spinners, six water holdup measurements electrical probes, and six gas holdup measurements optical probes. These characteristics qualified FSI to adapt to the complex characteristics of fluid profile/flow regime of deviated wells and horizontal wells. By reconstructing the fluid holdup profile and the velocity profile in the wellbore, the production profile in the wellbore can be better described, and then the postfrac rate can be evaluated. FSI logging revealed that the effective clusters are mainly concentrated in the middle and upper parts, and there is no obvious production seen in the lower part of each stage. Among the 72 clusters of Stage 6–9 covered by FSI (Stages 1–5 were not covered due to coiled tubing stuck), about 24 clusters effectively have production while the other 48 clusters do not. This means effective clusters account for about 33.3%. About 19 of 72 clusters have high production (more than 1% contribution of each cluster), accounting for approximately 26.4%, which proved that the operation of extra-long section extra-multicluster failed to achieve the desired effect of improving the complexity of fractures. The operation also failed to ensure fracturing fluid enters cluster evenly. In these nine fracturing stages, the gas production of Stage 1–5 accounted for only about 20%. The gas production of Stage 6 accounted for 17.7%. The gas production of Stage 7 and Stage 8 accounted for about 50%. And, the gas production of Stage 9 accounted for 13.9%. The relationship between production rate of each cluster in each specified stage and well deviation was established. The results show well deviation plays an important role during hydraulic fracturing and should be taken into consideration in future fracturing job design. Moreover, by combining with the production performance and the hydraulic fracturing parameters of each stage, this paper further points out the reasons why this novel fracturing technology does not achieve the desired effect. It describes the reasons for failed "temporary plugging turning" and offers guidance for long-stage multicluster fracturing technology in the future.